Method and device for loading fibers contained in a fibrous suspension with calcium carbonate

ABSTRACT

In a method and device for loading the fibers that are contained in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction, calcium oxide and/or calcium hydroxide are added to the fiber stock suspension. In order to trigger the precipitation reaction at least partially liquid carbon dioxide is injected into the reactor thereby ensuring the transformation of the starting substance calcium dioxide or calcium hydroxide into the reaction products calcium carbonate and water. The carbon dioxide can be added in an exclusively liquid state or partially in a liquid state and partially in a gaseous state.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation of prior PCT application No.PCT/EP02/01603, entitled “METHOD AND DEVICE FOR CHARGING FIBERSCONTAINED IN A FIBROUS SUSPENSION WITH CALCIUM CARBONATE”, filed Feb.15, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method and to a device forloading of fibers that are contained in a fibrous suspension, withcalcium carbonate by way of a chemical precipitation reaction.

[0004] 2. Description of the Related Art

[0005] Loading with an additive, for example a filler, can occur througha chemical precipitation reaction, especially through a so-called “FiberLoading™” process, as described in addition to other publications, inU.S. Pat. No. 5,223,090. In this type of “Fiber Loading™” process anadditive, especially a filler, is deposited onto the moistened fibersurfaces of the fibrous material. The fibers can for example be loadedwith calcium carbonate. Moreover, calcium oxide and/or calcium hydroxideare added to the moist, disintegrated fibrous material so that at leasta part of this associates itself with the water that is contained in thefibrous material. The so treated fibrous material is subsequentlytreated with carbon dioxide.

[0006] Hitherto gaseous carbon dioxide was always exclusively added tothe pulp in order to trigger the chemical precipitation reaction.

SUMMARY OF THE INVENTION

[0007] The present invention provides an improved method as well as animproved device for loading of fibers that are continued in a fibroussuspension, with calcium carbonate by way of a chemical precipitationreaction, which especially facilitates better control of the reactiontemperature.

[0008] The present invention comprises a method for loading the fibersthat are contained in a fiber stock suspension with calcium carbonate byway of a chemical precipitation reaction, whereby calcium oxide and/orcalcium hydroxide are added to the fiber stock suspension. In order totrigger the precipitation reaction at least partially liquid carbondioxide is injected into the reactor thereby ensuring the transformationof the starting substance calcium dioxide or calcium hydroxide into thereaction products calcium carbonate and water.

[0009] When adding the medium that contains the calcium oxide and/or thecalcium hydroxide to the fiber stock suspension, a chemical reactionwith exothermal characteristic occurs, whereby the calcium hydroxide isadded preferably in liquid form (milk of lime). The water that ispossibly embedded in or deposited on the fibers which are contained inthe fibrous stock suspension is not absolutely necessary for the startand conclusion of the chemical reaction.

[0010] Based on this configuration, the reaction temperature can becontrolled as desired by adding liquid carbon dioxide. The injectedliquid carbon dioxide is transformed in part into a gaseous medium andin part into a solid medium, dry ice. The solid medium consists of verysmall particles (particle mist) that have a diameter smaller than 3 mmand evaporate very quickly and transition from the solid state into thegaseous state. This is an exothermal process. Since dry ice, that issolid carbon dioxide possesses the ability to transition directly from asolid state into a gaseous state without going through a liquid phase,no energy expenditure is necessary in order to vaporize the liquidcarbon dioxide. The excess reaction energy can be utilized to convertcarbon dioxide from its solid state into the gaseous state. Not only isa new method for the production of calcium carbonate found, butespecially also an optimum sequence for the loading of fibers isachieved.

[0011] The carbon dioxide can be added exclusively in liquid form, orpartially in liquid form and partially in a gaseous form. If the carbondioxide is added partially in liquid form and partially in a gaseousform, then the reaction temperature and thereby the crystalline form isadjusted preferably through the ratio of the volume of the liquid carbondioxide component to the volume of the gaseous carbon dioxide component.

[0012] In accordance with an additional advantageous embodiment of thepresent invention the reaction temperature is regulated via thedifferential pressure P_(Δ)=P_(CO2)−P_(R) between the liquid carbondioxide and the reaction space where P_(R) is the pressure in thereaction space. The differential pressure P_(Δ) is selected preferablyso that it is within a range of 0<P_(Δ)<100 bar and preferably in arange of 1<P_(Δ)<50 bar.

[0013] If the reaction temperature is lower than or equal to 45° C. thena rhombohedral crystallite form of the precipitated calcium carbonateemerges. However, if this reaction temperature is higher than 45° C.then a scalenohedron crystallite form of the precipitated calciumcarbonate emerges. One or the other crystallite form can be achieved,depending upon in which range the reaction temperature is maintained.

[0014] The total requirement of added carbon dioxide that includes, forexample of a liquid and a gaseous component, results from astoichiometric consideration of the balance reaction:

Ca(OH)₂+Ca₂

CaCO₃+H₂O

CaO+H₂O+CO₂

CaCO₃+H₂O

[0015] Liquid carbon dioxide in pressure vessels, for example bottles,is normally under high pressure to approximately 300 bar.Advantageously, the carbon dioxide can now be relieved into the reactorchamber so that it cools down and in part becomes solid, in other words,transitions from the liquid state into the solid state of aggregationand ices up. This causes a cooling action whereby the temperature of theexothermic balance reaction is influenced accordingly.

[0016] The greater the gaseous carbon dioxide content (CO₂), as well asthe calcium hydroxide (Ca(OH)₂) content, are the greater the reactiontemperature can be, or vice versa. As already mentioned, thetemperature, or in other words the cooling action of the liquid carbondioxide can be regulated as desired through the ratio between the volumeof the liquid carbon dioxide content and the volume of the gaseouscontent, as well as through the differential pressure between the liquidcarbon dioxide and the reaction space. The larger the differentialpressure, the greater the cooling effect, as long as equal volumes ofcarbon dioxide are considered. The liquid or gaseous carbon dioxiderespectively is injected into the reactor advantageously through avalve.

[0017] When loading the fibers with calcium carbonate (CaCO₃) it isdeposited on the moistened fiber surfaces by adding calcium oxide (CaO)and/or calcium hydroxide (Ca(OH)₂) to the moist fiber material, wherebyat least a part of which can associate itself with the water of thefibrous stock volume. The thereby processed fiber material is thentreated with carbon dioxide (CO₂). The term “moistened fiber surfaces”may encompass all moistened surfaces of the individual fibers. Thisspecifically also includes the scenario where the fibers are loaded withcalcium carbonate or any other desired precipitation product on theiroutside surfaces as well as on their inside (Lumen).

[0018] Accordingly the fibers are loaded with the filler calciumcarbonate, whereby the loading onto the moistened fiber surfaces occursthrough a so-called “Fiber Loading™” process, as described in U.S. Pat.No. 5,223,090. In this “Fiber Loading™” process the carbon dioxide withthe calcium hydroxide reacts to water and calcium carbonate.

[0019] The present inventive device for loading of fibers that arecontained in a fiber stock suspension with calcium carbonate by way of achemical precipitation reaction accordingly includes elements throughwhich calcium oxide and/or calcium hydroxide can be added to the fiberstock suspension. It further includes a reactor and elements throughwhich at least partially liquid carbon dioxide can be injected into thereactor in order to trigger the precipitation reaction, thereby ensuringa transformation of the starting substances calcium oxide or calciumhydroxide into the reaction products calcium carbonate and water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above-mentioned and other features and advantages of thisinvention, and the manner of attaining them, will become more apparentand the invention will be better understood by reference to thefollowing description of an embodiment of the invention taken inconjunction with the accompanying drawing, which is a schematic view ofan embodiment of the present invention. The exemplification set outherein illustrates one preferred embodiment of the invention, in oneform, and such exemplification is not to be construed as limiting thescope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring now to the drawing, there is shown a purely schematicillustration of device 10 for loading of fibers 12 that are contained ina fiber stock suspension with calcium carbonate, by way of a chemicalprecipitation reaction.

[0022] Device 10 includes element 14 through which calcium oxide CaOand/or calcium hydroxide Ca(OH)₂ can be added to the fiber stocksuspension. Device 10 further includes a “Fiber Loading™” reactor 16, aswell as valve 18, through which the liquid carbon dioxide CO₂ can beinjected into reactor 16.

[0023] The carbon dioxide can be added exclusively in a liquid state orin part in a liquid state, and in part in a gaseous state. In the secondscenario an additional valve 20 is provided, through which gaseouscarbon dioxide CO₂ can be supplied to reactor 16.

[0024] Device 10 can include controller 22 for the adjustment ofreaction temperature T_(R) and ratio control 24 by way of which theratio (Vol_(liquid)/Vol_(gaseous)) of the volume Vol_(liquid) of theliquid carbon dioxide component and the volume Vol_(gaseous) of thegaseous carbon dioxide component is appropriately variable for acorresponding adjustment of reaction temperature T_(R). A ratiocontroller 26 can be provided that is actuated by ratio control 24 andthat determines the ratio of the flows through the two valves 18, 20 andcompares them with the desired value that was predetermined by ratiocontrol 24 in order to then adjust this ratio accordingly. Controller 22receives the actual value of, for example, reaction temperature T_(R)via a corresponding measuring device 28. This actual value is comparedwith a desired value 30 in the controller 22. Then ratio control 24 isaccordingly supplied in order to deliver an appropriate desired ratiovalue to ratio controller 26.

[0025] The reaction temperature is adjustable also through differentialpressure P_(Δ)=P_(CO2)−P_(R) between the liquid carbon dioxide and thereaction space in addition to being adjustable through the volume ratioof the liquid and the gaseous carbon dioxide components. Reactor 16 thensupplies fiber stock 32 that is loaded with, for example, calciumcarbonate CaCO₃.

[0026] Calcium oxide and/or calcium hydroxide (slaked lime) is added tothe fiber material in such a way that at least a portion of this canassociate itself with the water that is contained in the fiber material,i.e. between the fibers, in the hollow fibers and in their walls, thuscreating the following chemical reaction:

[0027] The fiber material is then treated with carbon dioxide (CO₂) inthe relevant reactor, so that calcium carbonate (CaCO₃) is extensivelydeposited onto the moistened fiber surfaces. This results in thefollowing chemical reaction:

[0028] While this invention has been described as having a preferreddesign, the present invention can be further modified within the spiritand scope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

Component Identification

[0029]10 Device

[0030]12 Fibers

[0031]14 Means for adding calcium oxide and/or calcium hydroxide

[0032]16 Reactor

[0033]18 Valve

[0034]20 Valve

[0035]22 Controller

[0036]24 Ratio control

[0037]26 Ratio controller

[0038]28 Measuring device

[0039]30 Desired value

[0040]32 Loaded fiber stock

[0041] P_(R) Pressure in the reaction space

[0042] T_(R) Reaction temperature

What is claimed is:
 1. A method for loading fibers in a fiber stocksuspension with calcium carbonate by way of a chemical precipitationreaction, comprising the steps of: adding at least one of a calciumoxide and a calcium hydroxide to the fiber stock suspension; injectingan at least partially liquid carbon dioxide into a reactor; andtransforimig said at least one of calcium oxide and calcium hydroxideinto a plurality of reaction products including calcium carbonate andwater.
 2. The method of claim 1, wherein said at least partially liquidcarbon dioxide is exclusively liquid carbon dioxide.
 3. The method ofclaim 1, wherein said at least partially liquid carbon dioxide includesa gaseous liquid carbon dioxide.
 4. The method of claim 3, furtherincluding the step of adjusting both a reaction temperature in saidreactor and a crystalline form of the calcium carbonate through a ratioof a volume of said liquid carbon dioxide to a volume of said gaseouscarbon dioxide.
 5. The method of claim 1, further including the step ofregulating a reaction temperature in said reactor via a differentialpressure P_(Δ)=P_(CO2)−P_(R) between said liquid carbon dioxide and areaction space in said reactor.
 6. The method of claim 5, wherein saiddifferential pressure P_(Δ) is approximately between 0 bar and 100 bar.7. The method of claim 5, wherein said differential pressure P_(Δ) isapproximately between 1 bar and 50 bar.
 8. The method of claim 1,further including the step of achieving a rhombohedral crystallite formof the calcium carbonate by keeping a reaction temperature in saidreactor no greater than 45° C.
 9. The method of claim 1, furtherincluding the step of achieving a scalenohedron crystallite form of thecalcium carbonate by keeping a reaction temperature in said reactorgreater than 45° C.
 10. The method of claim 1, further including thestep of cooling down said carbon dioxide by relieving said carbondioxide into said reactor thereby creating an at least partially solidcarbon dioxide.
 11. The method of claim 1, wherein said at leastpartially liquid carbon dioxide is injected into said reactor through avalve.
 12. A device for loading a plurality of fibers that are containedin a fiber stock suspension with calcium carbonate by way of a chemicalprecipitation reaction, comprising: at least one first adding elementthrough which at least one of calcium oxide and calcium hydroxide areadded to the fiber stock suspension; a reactor connected to said atleast one first adding element; and at least one second adding elementconnected to said reactor; said at least one second adding elementthrough which at least partially liquid carbon dioxide is injected intosaid reactor in order to trigger a precipitation reaction, therebytransforming said at least one of calcium oxide and calcium hydroxideinto a plurality of reaction products including a calcium carbonate andwater.
 13. The device of claim 12, wherein said at least partiallyliquid carbon dioxide is exclusively liquid carbon dioxide.
 14. Thedevice of claim 12, wherein said at least partially liquid carbondioxide includes a gaseous liquid carbon dioxide.
 15. The device ofclaim 14, wherein both a reaction temperature in said reactor and acrystalline form of the calcium carbonate are adjusted through a ratioof a volume of said liquid carbon dioxide to a volume of said gaseouscarbon dioxide.
 16. The device of claim 12, wherein a reactiontemperature in said reactor is regulated via a differential pressureP_(Δ)=P_(CO2)−P_(R) between said liquid carbon dioxide and a reactionspace in said reactor.
 17. The device of claim 16, wherein saiddifferential pressure P_(Δ) is approximately between 0 bar and 100 bar.18. The device of claim 16, wherein said differential pressure P_(Δ) isapproximately between 1 bar and 50 bar.
 19. The device of claim 12,wherein a rhombohedral crystallite form of the calcium carbonate isachieved by keeping a reaction temperature in said reactor no greaterthan 45° C.
 20. The device of claim 12, wherein a scalenohedroncrystallite form of the calcium carbonate is achieved by keeping areaction temperature in said reactor greater than 45° C.
 21. The deviceof claim 12, wherein said carbon dioxide is relieved into said reactorcooling said carbon dioxide thereby creating an at least partially solidcarbon dioxide.
 22. The device of claim 12, wherein said at leastpartially liquid carbon dioxide is injected into said reactor through avalve.